1. Technical Field
This invention relates to the field of medical devices, and more particularly, to an introducer sheath for use in deploying an expandable medical device into a body passageway of a patient.
2. Background Information
Numerous advances of considerable note have occurred in medical surgical techniques over the last few decades. Among the most significant advances has been the adoption, and now-routine performance, of a wide variety of minimally invasive procedures. When carrying out such procedures, access to a site of concern within a patient is achieved through a relatively small incision, into which a tubular device (such as a sheath) is inserted or introduced. The sheath keeps the incision open while permitting access to the target site via the interior (i.e., lumen) of the sheath. Non-limiting examples of such devices include introducer sheaths, guide catheters, and like devices (devices collectively referred to herein as “sheaths” or “introducer sheaths”).
Body passageways in which medical interventional devices, such as stents, are now commonly introduced include the esophagus, trachea, colon, biliary tract, urinary tract, and vascular system, among other locations within the body. When placing a medical interventional device in a passageway, communication with the passageway is typically attained by initially inserting the distal end of introducer sheath into the body passageway. Since the introducer sheath must often traverse tortuous pathways to reach the target site, the sheath often includes a coil reinforcement to facilitate passage through the pathways without kinking. Examples of introducer sheaths of this type are described in U.S. Pat. No. 5,380,304, and U.S. Pat. Publ. No. 2001/0034514, both incorporated by reference herein. The sheaths described in these patents include a lubricious inner liner having a helical coil fitted over the liner. An outer tube is connected to the outer surface of the liner through the coil turns. The coil reinforcement imparts kink resistance to this thin-walled sheath through a wide range of bending.
Another example of an introducer sheath is provided in U.S. Pat. No. 5,792,124, incorporated by reference herein. This patent discloses an introducer sheath having a woven braid as a reinforcing member. Although braided and coiled structures are now routinely used as reinforcements in tubular medical devices, those skilled in the art recognize that these reinforcements are not generally considered interchangeable. A coil is typically utilized in a sheath to minimize the possibility of the sheath kinking, and/or to minimize ovalization of the sheath lumen during bending of the sheath. On the other hand, a braid is typically utilized when it is desired to impart stiffness, pushability, or torqueability to the sheath.
The medical interventional device, such as an expandable stent, etc., is delivered to the target site from a lumen in the introducer sheath. Typically, the device is positioned at the target site by withdrawing the introducer sheath from around the stent while the stent is in a constricted condition. An inner catheter may be provided in the sheath lumen for preventing the stent from withdrawing with the sheath. In an alternative arrangement, the constricted stent may be pushed from the distal end of the sheath by a pusher mechanism positioned in the sheath lumen. In either technique, upon deployment at the target site, the device expands to the diameter of the surrounding body passageway.
Deployment of expandable devices, such as stents, in this manner is now a routine practice, and such deployment is often carried out with only a minimum of complications, if any. This is particularly true when the device has a relatively short length (e.g., less than about 80 mm) and/or a relatively modest outer diameter. However, as medical technology has progressed, stents and other interventional devices having longer lengths (e.g., about 100 to 300 mm or more) and/or having outer coatings, coverings, etc., that increase the effective outer diameter of the stent have become more common. When such stents are placed in a sheath lumen for delivery to the target site, the greater length and/or outer diameter of such stents increases the deployment forces necessary to extract the stent from the sheath when compared to shorter and/or lesser diameter stents. This increase in deployment forces is due primarily to the increased outward forces exerted by the longer and/or greater diameter devices on the interior wall of the sheath.
In this event, an introducer sheath having a coiled reinforcement has a tendency to stretch longitudinally as it is withdrawn from around the interventional device. Although this phenomenon may occur to a lesser degree with non-coated, non-covered, or shorter interventional devices, it is more pronounced with the coated, covered, or longer diameter devices. With such coated, covered or longer diameter devices, the stretching of the sheath causes the distance between adjacent turns of the coil to increase. This longitudinal expansion of the reinforcing coil adversely affects the ability of the sheath wall to withstand the radial expansive forces exerted on the interior of the wall by the stent, which may result in pockets being formed in the sheath wall between adjacent coil turns. When this occurs, surfaces of the undeployed stent may expand into such pockets, thereby undesirably increasing the resistance imparted by the stent upon the sheath, and hindering efficient deployment of the stent. In addition, the sheath may elongate as it is withdrawn from the stent. When such elongation occurs, the distance the sheath handle is capable of traveling upon deployment is reduced. A limited travel path for the sheath holder may present the stent from being fully deployed from the sheath into the vessel.
A sheath having a braid reinforcement is also prone to longitudinal stretching, or elongation, upon withdrawal from the stent, due to the increased deployment forces exerted on the sheath wall. With a braid reinforcement, such elongation reduces the inner diameter of the sheath to an extent that the stent cannot be efficiently extracted therefrom, if possible at all. Alternatively, such elongation may necessitate the use of a larger diameter sheath than may be desired, so that the stent can still be deployed therefrom in light of the expected elongation and reduction in diameter of the braided sheath upon use.
It is desired to provide an improved introducer sheath or other medical apparatus suitable for traversing tortuous passageways in the patient's anatomy during deployment of a medical interventional device, such as an expandable stent. More particularly, it is desired to provide an introducer sheath that is capable of minimizing elongation or stretching during withdrawal of the sheath from a medical interventional device, thereby providing for more efficient withdrawal of the sheath when used to position the interventional device in a body passageway.